The present invention relates to a microcircuit testing device.
More particularly, the device relates to a device for testing integrated circuits, or microcircuits, and particularly to methods for manufacturing devices whereby said integrated circuits, before splitting a silicon wafer, are placed in electrical contact with the testing device.
It is known that the devices commonly used to test a silicon wafer by connecting simultaneously all the pads of the microcircuit to the device, commonly known as probe cards, are constituted by a printed circuit board having variable shapes and complexities, which is provided with a hole also having various shapes and into which elastic metallic needles, known as probes, protrude, the tip of said needles making contact with a pad of the microcircuit.
Automatic alignment and movement systems ensure that each microcircuit that is present on the silicon wafer is sequentially arranged so as to face the hole of the probe card and is moved towards it, so that each probe tip makes contact with the respective pad.
Among the various probe assembly systems of the prior art, the one most widely used for applications with a high density of probes per microcircuit is disclosed by U.S. Pat. Nos. 3,835,381 and 3,905,098 in the name of Garretson et al and is duplicated with minor variations in other documents.
This system provides for probes made of tungsten or copper-beryllium or other conducting materials, arranged so as to form a radiating array along the generatrices of a frustum-shaped ring whose apex angle is almost flat; the tips of said needles are directed towards the center of the ring and bent downward. The probe supporting ring is usually made of materials which are as temperature-stable as possible, in order to allow maximum positioning constancy for the probe tips.
The probes are locked in position by pouring a resin which also has the best possible characteristics in terms of thermal stability and electrical insulation.
Conventional microcircuit testing devices, however, are affected by some drawbacks which are described hereinafter.
Use of a printed circuit board as a support for the probe supporting ring entails problems in terms of limited mechanical rigidity which are inherent in the material, which is usually epoxy resin embedding a mat of glass fiber.
Moreover, the conventional almost-horizontal arrangement of the needles, i.e., approximately parallel to the probe card, has some shortcomings if simultaneous probing of a plurality of microcircuits is required.
This is particularly necessary for example in the testing of memory microcircuits, in which case it is necessary to probe two, four or more columns, each bearing four, eight or more microcircuits arranged side by side, as shown schematically in FIG. 1, which illustrates by way of example the simultaneous probing of four columns, each composed of two microcircuits.
In FIG. 1, the reference numeral 50 designates a silicon wafer and the reference numerals 51/52, 53/54, 55/56 and 57/58 designate respectively the pairs of microcircuits arranged side by side which must be tested by the testing device.
Also in the most favorable case, in which each microcircuit has contact pads arranged along a single median row, as shown in FIG. 2, which is an enlarged-scale detail view of the four pairs of microcircuits shown in FIG. 1, with the probes designated by the reference numeral 60, which make contact with respective pads, designated by the reference numeral 61, of the microcircuits arranged side by side, the probe system with horizontal needles (probes 60) limits to two the number of columns that can be contacted. If one wishes to access more than one row of pads 61 from either side of the ring, the difference in length of the probes between one row and the next would have to be approximately equal to the pitch between the columns, producing needles 60 having considerably uneven lengths, with a great difference in the elastic contact forces, making it therefore impossible to obtain uniform contact resistances among the probes 60.